Probe measurements at higher pressure

Existing theories and previous probe measurements of electron distribution functions (EDF) at higher gas pressure are reviewed. An explanation of whether or not the measurements are realizable and reliable, an enumeration of the most common sources of measurement error, and an outline of proper probe-experiment design elements that inherently limit or avoid error are presented. Recent EDF-measurement developments in higher-pressure plasma conditions, including electron spectroscopy analysis with a large wall probe, are discussed. A short (without positive column) dc discharge with cold cathode and conducting walls was used in experiments at gas pressures of a few Torrs. For the investigated conditions, the plasma is collisional. It is experimentally shown that the EDF is proportional to the second derivative of electron current with respect to the probe potentials (as in collisionless theory). EDF measurements conducted in Helium-Argon gas mixtures with percent composition of Argon from 0.002% to 5% will be presented, as will the demonstration of current-voltage calibration.